Cooking under vacuum is a cooking technique for foodstuffs that consists of cooking—at temperatures usually comprised between 70 and 100° C.—foodstuffs previously placed into specific packages or packets made of polymer material. These packages or packets are typically polyethylene bags with external nylon covering, wherein vacuum has been previously obtained by suitable means.
The cooking of such foodstuffs can be carried out in a humid environment (e.g. by boiling), in a steam oven or microwave oven.
One particular feature of this type of cooking is that there is no direct contact between the cooked foodstuffs, which are contained in the package under vacuum, and the cooking means. This allows avoiding losses of water from the foodstuffs, which thus preserve their tenderness as well as many other desired characteristics.
Other advantages are obtained with this type of cooking. Cooking under vacuum also avoids direct contact of the foodstuff with external contamination sources and therefore ensures greater sanitary-hygienic safety. The preservation time of cooked foodstuffs is also extended up to 20 days if, after cooking, the foodstuffs are preserved in their package under vacuum at temperatures lower than 3° C.
In order to be sure that a foodstuff is correctly cooked under vacuum, it is necessary to verify that the so-called “core” temperature of the foodstuff, i.e. in the most inner part thereof, reaches and maintains a temperature of about 90° C. for a specific time interval. This assessment is carried out during foodstuff cooking by means of temperature sensor means, e.g. a needle probe, which is inserted through the package until it penetrates into the foodstuff contained therein, in order to measure the temperature thereof.
In order to ensure the maintenance of the fluid tight characteristic of the package containing the foodstuff, even after the penetration of the needle probe, which pierces the package during the temperature measurement, a so-called fluid tight tape is previously applied on the package, at the point where the probe is expected to pierce the package. Such fluid tight tape is typically a strip of material with adhesive surface applied to the package and equipped with sufficient heat resistance and elasticity such as to elastically yield, so that once the needle probe has been removed from the package, the tape automatically tightly closes the hole formed by the probe in such a way that the entrance of air into the package is prevented. Examples of material used for obtaining this type of tape are expanded silicone and neoprene. Thanks to such a fluid tight tape, the package is maintained fluid tight even after repeated insertions/removals of the temperature needle into/from the package.
The limit of this type of tape is the fact that, since it is typically made of non-adhesive materials, one must provide for a glue means on the contact surface of the tape with the package in order to ensure, in use, a perfect adherence to the package. There is the risk that, during the step of temperature measurement, while the probe penetrates the tape, the glue and the package, it brings some glue with it inside the package, with foodstuff contamination effects.